import java.util.Scanner;

abstract class RR{
int[] grade;
public RR(int[] grade){
this.grade = grade;
}
public abstract double mark();
}
class RT extends RR{


public RT(int[] grade) {
super(grade);
}

public double mark(){
double x = (grade[1]+grade[2]+grade[3])/3;
return x;
}
}
public class Main {

public static void main(String[] args) {
@SuppressWarnings("resource")
Scanner in = new Scanner(System.in

);
int[] grade = new int[5];
for(int i=0; i<grade.length; i++){
grade[i] = in.nextInt();
}

RR rr = new RT(grade);
double dd = rr.mark();
System.out.printf("%.2f",dd);
}

}